Maybe someone can help me understand why a certified testing company would recommend both RH and calcium chloride testing on the same job, considering the "risk" that a key decision maker would likely opt to use the more preferable (lower reading) test results to base their decision to install floor coverings.

I always recommend the RH test method for all the reasons we already know, and have only conducted one calcium chloride test in the last 2 years. To me, this is a no brainer.

Scenario: I was just asked about two slabs this week. Both are in the mid to upper 90's rH.

One slab had an MVER of around 3lbs. The surface was burnt black and had a curing compound applied immediately after the pour. The slab was in an enclosed building, so I question if the self-dissipating curing agent ever dissipated. Most of these need some UV light to break down.

The other slab was porous and had an MVER of almost 10lbs.

Here's where the thinking went awry... The person with the 3lb slab thought his slab was dry enough, or very nearly dry enough, while the person with the 10lb slab thought theirs would never dry. Remember both were over 93% rH.

The company with the 3lb slab was willing to continue waiting for the rH to drop, and the company with the 10lb slab was ready to throw in the towel immediately!

I explained to mr. 10lb slab that his high MVER was showing the slab was drying at a rapid rate, over a gallon of water per day per 1000sf in fact. If he can promote drying like that, he may drop the rH quickly. But the 3lb slab is holding water and will take nearly forever to dry. (Forever in flooring speak is > 2 weeks ).

Another kicker in this story was the CaCl tests were done improperly and the surfaces weren't prepped right. In this case though, when you are measuring the actual concrete surface that you will be gluing to, I think you gain some important knowledge.

CaCl tests can also indicate a recent wetting or flooding of a concrete floor which the rH test will not pick up.

Yea we don't accept CaCl tests anymore. Even people with a P.E. after their name seem to not be able to do it correctly. These pictures done by one of the more respected "professional building testing labs" in California.

Here is an example of this.

side note: oy the cracks Lumpy Bumpy Slab will probably break poor church's budget. We want to fix the crack with Roadware Concrete Mender but at over $5 lft it is so expensive.

Used ArdiFix myself...good stuff. I like the ArdiBond too
I think CC was implying they were basically resistant to breakdown from moisture vapor emissions and high RH, not moisture proof. Big difference.
While we're in the 2% doing it right, the tricky part is educating the masses that most are testing improperly and putting installations at risk. Every architectural spec (and property owner/client) would benefit by requiring that testing be performed only by ICRI Certified, independent testing agencies or technicians. There would be a lot less failures and litigation.

I agree, CCR...I wish that all my projects required the testing to be done by an independent, certified agency.

Not only is it beneficial to owners and clients, but to us as contractors as well. I would much rather not be in the position of monitoring the RH of a slab which is waiting for flooring installation, and having the GC question my every move, asserting that my testing MUST be faulty (because the 5" slab that he poured 6 weeks ago is testing in the high 90% and not moving down by leaps and bounds every day **eyeroll**).

Even when you educate them, when they are being ridden by (an unrealistic) schedule, they seem to not get it.

I believe if the testing was done independently, they would have a harder time pressuring us to install the flooring before the concrete is ready.

Totally agree. Too bad that human nature plays such a role in placing doubts on your professionalism and intentions. Unfortunately, I have found too many GC job site supervisors suspicious by nature. I'm sure many have been burned and even fired over things out of their control (like concrete drying). Installers are much better off bringing in the independent testing agency to test and be the bearer of bad news rather than appearing uncooperative with the GC and risking future installation business!